|ITALIAN RADIATION PROTECTION ASSOCIATION
COMMENTS ON THE
RECOMMENDATIONS OF ICRP
Since ICRP began the revision of its 1990-1991 Recommendations with the 2002 document and encouraged radiation protection associations and experts to communicate their views to the Commission, the Italian Radiation Protection Association (AIRP) has been following the ICRP process of revision closely; to this end a Working Group was set up with the remit to review the new ICRP Draft Recommendations and to submit comments.
As a result of the ICRP process of revision of the 2005 Draft Recommendations, which were made available for comments by, inter alia, associations of professional radiation protection experts, the Commission has recently made known the 2006 Draft of its new Recommendations. AIRP submits the following views and comments of its Working Group on the 2006 Draft Recommendations with a view to contributing to the Commission's efforts in ensuring that the future ICRP Recommendations are well understood and applied.
The AIRP Working Group welcomes the Commission's openness in making the 2006 Draft of its Recommendations available for comments as well.
The AIRP Working Group finds highly commendable that the philosophy underlying the 2006 Draft is a really positive and pragmatic evolution in respect of the 1990 Recommendations, acknowledging the need for stability in the ICRP radiation protection framework and its implications on regulatory systems worldwide. The Working Group also must state its appreciation for the thorough revision of the 2005 Draft carried out by the Commission.
The Working Group notes that there still remain some seemingly unresolved issues in the Draft in that some aspects require harmonisation from the point of view of "internal" consistency within the Draft as well as between the Draft, on the one side, and Annexes A and B and "building blocks" documents, on the other side. Attention is called to some of these aspects in the Working Group's comments together with further views and suggestions.
The principle of justification
The Working Group welcomes the fact that the Commission chose to bring in the justification principle in the 2006 Draft Recommendations, albeit the Commission wisely recognises that justification is ultimately a governmental responsibility to which radiation protection considerations are just one of the inputs.
Since the justification principle is a very useful tool in the decision process, it is felt that the Commission should give guidance on methods and instruments through which radiation protection considerations can be factored in as inputs with a view to weighing alternatives when decisions are to be made.
In respect of the way the justification principle is addressed in the 2006 Draft Recommendations there are some perceived variations within the Draft for which clarification by the Commission is called for, e.g. what is the role of societal interests and collective dose versus interests of, and doses to, individuals in the context of the justification principle. Please see the section of this document on Specific Comments.
Scientific bases of the Recommendations
The Working Group is well aware of, and appreciates, the great deal of scientific toil that was required of the Commission, its Committees and Task Groups in order to make Annexes A and B as well as "building blocks" documents available for comments. Thus, the wealth of information published by ICRP makes the Commission's thinking easier to understand.
In particular, it is felt that ICRP must be commended for Annex A, since the manifold, complex issues underlying so sophisticated a subject as estimates of health risks of radiation were addressed clearly so that the core logic could be grasped by any expert with a scientific education in radiation protection, even without a specialist's knowledge in radiobiology and epidemiology.
The fundamental radiation protection quantity, effective dose
In respect of radiation protection quantities, the Working Group notes that in the 2006 Draft the Commission repeatedly warns against nominal risks coefficients and protection quantities being used for assessments of a retrospective or epidemiological nature. As a matter of fact, ICRP emphasises that, for the reasons stated with clarity in the Draft and in the Annexes, such quantities and coefficients are only meant to be employed prospectively for control purposes.
In this respect the Working Group considers that, on the one hand, an ideal protection system would certainly be the one availing itself of the same array of quantities and methods for both prospective and retrospective assessments of radiation risk.
On the other hand, the Working Group acknowledges that expert judgment is called for in defining radiation protection quantities since the present state of knowledge on low dose radiation effects does not allow for both utmost scientific rigour and a practicable and efficient protection system.
The Working Group is fully aware of the manifold assumptions, uses of judgment and simplifications implied in the definition of radiation protection quantities, in particular as regards effective dose.
However, even though due account must be taken of the limitations in the use of effective dose owing to the reasons clearly stated by the Commission, the Working Group points out that there is a seemingly serious flaw in the ICRP system: indeed, ICRP recommends the use of effective dose for the control of radiation exposures, i.e. compliance with dose limits, then warns that the use of this quantity may not be appropriate when effective dose is above, or close to, dose limits. In other terms, the quantity should not be fully relied upon to verify compliance with the very dose limits that are a reason for its definition. Please see the section on Specific Comments of this document.
Dose constraints, exclusion values
Owing to the ICRP recommendation on the appropriateness of the use of effective dose in the proximity of dose limits, the Working Group feels that a discussion in terms of risk is in order as regards the choice of recommended dose constraints.
Another aspect that the Commission would do well to expand upon are the exclusion values recommended for natural radionuclides, for which a discussion in terms of balance between risks and amenability to control is felt to be missing.
Protection of non human species
The Working Group appreciates the soundness and pragmatic approach of the Commission's stance on protection of the environment in Chapter 10. It is to be hoped that scientific developments in the future will warrant further advice on the use to be made of the Commission's recommended models for Reference Animals and Plants.
Text of the Recommendations
The inclusion of Glossaries in the 2006 Draft Recommendations and in Annexe A was much appreciated; in this context, it is felt that the Commission would do well in including an Index in the future Recommendations.
"(16) ... The use of models has resulted in the derivation of practical, tabulated information on the anticipated ‘dose per unit intake’ of different radionuclides that can be applied to workers, patients and the public." (Bold in the quotation above is the AIRP Working Group's)
The AIRP Working Group notes that in paragraph (16) the Commission uses the term 'anticipated dose for unit intake' instead of the time honoured correct term "committed dose".
Since it is felt that any changes in terminology should be kept to a minimum and unnecessary changes ought to be avoided altogether, the Working Group suggests that "committed dose" should be substituted for "anticipated dose per unit intake."
Paragraphs 17, 18, 140, 122
"(17) ... then the estimates of fatality and detriment coefficients are adequate both for planning purposes and for general prediction of the consequences of exposures of a nominal population. For the estimation of the likely consequences of an exposure of an individual or a known population, it is preferable to use absorbed dose, specific data relating to the relative biological effectiveness of the radiations concerned, and estimates of the probability coefficients relating specifically to the exposed individual or population."
"(18) The system for assessment is robust and is, in several aspects, in conformity with what is used in other fields of environmental protection, e.g. the identification of health hazards (from all radiation sources), characterisation of the relevant biological processes (primarily through DNA damage) and risk characterisation involving reference values."
"(140) The main and primary use of reference values of effective dose is to provide a means of demonstrating compliance with dose limits. In this sense effective dose is used for regulatory purposes worldwide. In practical radiological protection applications, effective dose is used for the control of radiation exposures of workers and for dose records. This is appropriate as long as the effective dose is close to or below dose limits."
"(122) For the monitoring of external exposures, various operational dose equivalent quantities have been defined by ICRU. ... Dose equivalent quantities are measurable quantities and instruments for radiation monitoring are calibrated in terms of these quantities. In routine monitoring the values of these dose quantities are taken as a sufficiently precise assessment of effective dose and skin dose, respectively, in particular, if their values are below the protection limits." (Bold in the quotations above is the AIRP Working Group's)
As stated in the section on General Comments of this document, the Working Group is fully aware of the manifold assumptions, uses of judgment, simplifications and operations of averaging that are implied in the definition of radiation protection quantities, in particular as regards effective dose, the use of which is recommended by ICRP for prospective estimates only.
This said, the Working Group feels that ICRP's recommending the use of effective dose in paragraph (140) as appropriate for control purposes "as long as its value is close to or below dose limits" is a cause for worry, and there are a number of issues that call for further clarification and guidance by the Commission.
As regards the use of effective dose the situation might be summed up in plain English as follows: for control purposes the ICRP system recommends a quantity, effective dose, in which dose limits, and dose constraints for that matter, are set out; yet, the Commission warns against its use being appropriate if values of effective dose are above, or close to, the very dose limits expressed in terms of this very quantity.
Again, as seen from a layman's point of view, the Commission recommends a quantity, in which dose limits and constraints are expressed, that is not thought to be fully reliable in proximity to the very dose limits for which the use of the quantity is intended.
Accordingly, this fact is likely to provoke a disturbing lack of confidence in the main quantity of the ICRP protection system, besides shedding a disturbing light of instability on the system, which cannot be said to be "robust" at least in this respect.
At least as concerns the Draft, no explicit reasons are specifically stated for these words of caution by ICRP on the use of effective dose for control purposes when its values lie in proximity to dose limits. Such reasons may be traced back, though, to the manner effective dose is defined by ICRP. In fact, the quantity effective dose is defined, amongst other things, for a reference individual through a series of assumptions, applications of judgment, simplifications and operations of averaging. Owing to these facts, effective dose cannot be thought to be a fully adequate measure of risk for a specific individual.
However, stating that effective dose cannot be used for retrospective analyses or for estimates of health consequences in a specific individual or in a specific population is markedly different from warning, as ICRP does, against the use of the quantity for verifying compliance with limits if effective doses are above, or close to, dose limits and, for that matter, maximum values of dose constraints. If this line of reasoning is followed through to its ultimate consequences, it goes without saying that a good deal of problems may arise.
Firstly, there is the problem of what regulators and operators would be supposed to do in such circumstances (i.e., values of effective dose being close to, or above, dose limits or maximum values of dose constraints) in order to verify compliance and to allay fears by concerned parties that an unreliable quantity is used for their protection. How to assuage fears that the very assessment of compliance with dose limits, and with dose constraints for that matter, is not to be relied upon or, again in a layman's blunt terms, is not to be 'trusted' since limits and constraints are expressed in terms of effective dose?
Secondly, which dose limits does ICRP have in mind in the statement in paragraph (140)?
In point of fact, it is by no means clear which dose limits ICRP is addressing in paragraph (140). If it is dose limits for workers that are addressed, then the question turns into which dose limits the Commission has in mind: 20 mSv per year, 50 mSv per year, or 100 mSv in 5 years, or all of them. What is the rationale in choosing to refer to "dose limits" in such a vague way?
Thirdly, the Commission does recommend dose limits for members of the public as well. Accordingly, a further question is why control of exposures of the public is not mentioned in paragraph (140).
Fourthly, if the statement in paragraph (140) is to be followed through to its ultimate logical consequences, then the ICRP warning on effective dose not being adequate in proximity to dose limits holds for the maximum values of dose constraints equally well, all the more so that the highest value of all recommended dose constraints is 100 mSv, way above any dose limit.
If effective dose is not adequate for verification of compliance near dose limits neither is effective dose adequate for verification of compliance with the 100 mSv dose constraint, which is applicable for acute or yearly exposures in case of emergency and existing situations.
Owing to the manner protection quantities are defined, it is obvious that they are only to be employed in the low dose range. Now, this range is not explicitly specified by ICRP although it must be noted in this respect that the Commission does state in paragraph (202) that, for protection purposes, the assumption of linearity applies up to acute or annual doses of about 100 mSv, with a view to limiting the occurrence of stochastic effects and avoiding deterministic effects. As a result, one would expect to be able to use protection quantities 'safely', at least up to a 100 mSv level of effective dose.
In addition, the misgivings above are compounded by the last sentence in paragraph (122), where ICRP specifies that operational quantities, which are defined as a function of Q(L), can be depended upon to provide a "sufficiently precise assessment" of effective dose, and skin dose at that, if their values are beneath protection limits. Again, which protection limits are addressed by ICRP in this context is entirely left unspecified, neither is any light shed in this regard by paragraphs 4.2 to 4.4 of Annex B on operational quantities for external exposures.
As regards equivalent dose to the skin in particular, if the statement in paragraph (202) is taken as its literal meaning would suggest, it would accordingly appear that the relevant operational quantities for skin, personal dose equivalent, Hp(0.07), and directional dose equivalent, H'(007, ), should be depended upon to provide a reliable assessment of equivalent dose (to the skin) below about 500 mSv, i.e., the relevant equivalent dose limit to the skin for workers. In this connection, though, a reader is left wondering how paragraph (202) must really be understood if the guidance on deterministic effects in paragraph (52) is taken account of, since in the absorbed dose range up to around 100 mGy (low LET or high LET) deterministic effects are not thought likely to appear. In other terms, the question is up to which dose level can operational quantities be thought of being a "sufficiently precise assessment" of skin dose.
By implication, the further question is up to which level the equivalent dose quantity can be used, since the 'safe' threshold level for deterministic effects lies in the vicinity of 100 mGy and dose limits set out in terms of equivalent dose to some organs or tissues reach 150/500 mSv.
Given the paramount importance of protection and operational quantities, which are simply vital for applying the ICRP system, the Working Group is firmly convinced that the future Recommendations and Annexes cannot afford in the least to be vague as regards the conditions in which and the range over which such quantities are reliably to be used. Neither can the Commission afford, in the Working Group's view, to be vague on the methods to utilise for control purposes in the cases where protection and operational quantities are not thought to be a dependable measure of radiological risk; accordingly, it is believed that detailed guidance to this effect should be given by ICRP, perhaps in an ad hoc publication.
In this connection, the Working Group also believes that the Commission should take due account of the risk that confidence by workers and the public in the ICRP recommended system of quantities, limits and constraints might be shaken in that regulatory limits, and constraints for that matter, are expressed, in particular, in terms of effective dose.
For the reasons stated above, the Working Group is convinced that the Commission should clarify its thinking and, at the very least, provide clear and detailed guidance on the use and limitations of protection quantities, and effective dose in particular, as a tool to insure compliance with dose limits and constraints.
Paragraphs 30 first bullet, 185 first bullet, 190, 293, 345, 347
"(30) (185).... The principle of justification: Any decision that alters the radiation exposure situation, e.g., by introducing a new radiation source or by reducing existing exposure, should do more good than harm, i.e., yield an individual or societal benefit that is higher than the detriment it causes."
"(190) In both approaches, the responsibility for judging the justification usually falls on governments or government agencies to ensure an overall benefit in the broadest sense to society and thus not to each individual. Radiological protection considerations will be important to a greater or lesser extent depending upon the circumstances."
"(293) The Commission recommends that the radiological protection systems should include natural sources of exposure in a coherent and consistent way taking into account the feasibility of control and the perceived demands of those affected."
"(345) The decision maker should determine whether the protective action is justified from the viewpoint of those individuals who are the most at risk. After that, consideration should be given to justification of the action from society’s point of view, because the costs and benefits will probably not be evenly distributed amongst the same people. The societal considerations may extend the protective action to cover an even larger group of affected people, or they may set limits to the practical or financial feasibility of the action (e.g. evacuation of a large city). In case the proposed protective action is not justified from the viewpoint of the individual, decision makers may still seek to reduce the collective dose and the detriment, and care should be taken not to do more harm than good in the process."
"(347) The introduction of any particular protective action entails some risk to the individuals affected and some harm to society in terms of financial costs and of societal and economic disruption. Therefore, before introducing a protective action, it should be shown that it can produce a positive net benefit." (Bold in the quotations above is the AIRP Working Group's)
The Working Group is aware that in the coming Recommendations the Commission intends to put emphasis on equity based considerations for the protection of individuals more than in the past; accordingly, less emphasis seems to be put on societal aspects of protection and related tools like collective dose.
The Working Group notes that the statement of the justification principle in paragraphs (30) and (185) is of a general nature and is thought to apply to the three types of exposures considered by the Commission: planned, emergency and existing situations. This said, the three paragraphs (30), (185) and (190) above do not seem to be wholly consistent: in paragraphs (30) and (185) society's protection needs seem to be on an equal standing with protection of the individual; in paragraph (190) societal protection needs are presented as overriding.
Also, in paragraph (345) protection of the most exposed individuals regains the first rank with societal protection needs being put on a secondary footing; since paragraph (345) addresses the application of the justification principle in case of emergencies and existing exposures, the Commission's advice certainly has merits, especially in emergency situations, given the need to avoid serious deterministic effects and high risks of stochastic effects in the individuals affected.
As regards existing and emergency exposures, on the other hand, the guidance in paragraph (345) does not accord with that given in paragraphs (30) and (185) and paragraph (190), the more so that the justification of a protective action is seemingly related in paragraph (347) to the objective of reaching a positive net benefit to individuals and society that appear to be on the same standing in this connection.
Besides, there is another aspect worth mentioning as regards paragraph (345); the way that the application of the principle is worded for emergency and existing exposures, i.e. "from the viewpoint of those individuals who are the most at risk", might engender doubts that entirely subjective viewpoints, viz the perception of risk by the individuals concerned, are to be of paramount importance in making decisions.
As far as the latter aspect is concerned, doubts are compounded by the wording of the Commission's statement in paragraph (293) that radiological protection systems should take into account, inter alia, the "perceived demands of those affected" as regards exposure to natural sources. Again, wholly subjective viewpoints of the individuals affected seem to be given overriding importance.
May the AIRP Working Group point out that these doubts and seeming variations originate from the Commission's policy of stating one set of principles intended to be valid in one and the same form for planned exposures on the one side and emergency and existing exposures on the other side.
The Working Group suggests that the Commission should review in a comprehensive way and clarify the statements quoted above. Also, the Working Group believes on the whole that more emphasis should be put by the Commission on aspects of societal benefit when stating the principle of justification.
Paragraphs 48, 49
"(48) The adverse health effects of radiation exposure may be grouped in two general categories:
• tissue reactions (also called deterministic effects) due in large part to the killing of cells at high doses; and
• cancer and heritable effects (also called stochastic effects) involving either cancer development in exposed individuals due to mutation of somatic cells or heritable disease in their offspring due to mutation of reproductive (germ) cells."
"(49) In Publication 60 (ICRP, 1991b) the Commission classified the radiation effects that results in tissue reactions as deterministic effects and used the term stochastic effects for radiation-induced cancer and heritable disease. Effects caused by injury in populations of cells were called non-stochastic in Publication 41 (ICRP, 1984), and this was replaced by the term deterministic, meaning ‘causally determined by preceding events’ in Publication 60 (ICRP 1991). The generic terms, deterministic and stochastic effects, are not always familiar to those outside the field of radiological protection. For this and other reasons (see Annex A) Chapter 3 and Annex A use the directly descriptive terms tissue reactions and cancer/heritable effects respectively. ... " (Bold in the quotations above is the AIRP Working Group's)
The Working Group appreciates that the Commission now allows for the use of the terms "deterministic effect" and "tissue reactions" interchangeably in that this choice makes for stability and unnecessary changes ought to be avoided in terminology as well.
In connection with the term "tissue reactions" it might be argued, though, that the reasons stated in Annex A for adopting the term "tissue reactions", i.e. the existence of response modifiers, are not entirely convincing because there exist therapeutic response modifiers that can alter the development even of cancer.
Paragraphs 50, 52, 53, Glossary
"(50) The induction of tissue reactions is generally characterised by a dose-threshold. The reason for the presence of this dose-threshold is that radiation damage (serious malfunction or death) of a critical population of cells in a given tissue needs to be sustained before injury is expressed in a clinically relevant form. Above the dose-threshold the severity of the injury, including impairment of the capacity for tissue recovery, increases with dose."
"(52) ... However, for the purposes of radiological protection, in the absorbed dose range up to around 100 mGy (low LET or high LET) no tissues are judged to show radiosensitivity that is sufficient to allow the dose-threshold for clinically relevant functional impairment to be exceeded. This judgement applies to both single acute doses and to situations where these low doses are experienced in a protracted form as repeated annual exposures."
"(53) Annex A provides updated information on dose thresholds (corresponding to doses that result in about 1% incidence) for various organs and tissues."
"(Glossary) Deterministic effect: A health effect of radiation for which generally a threshold level of dose exists above which the severity of the effect is greater for a higher dose. Such an effect is described as a ‘severe deterministic effect’ if it is fatal or life threatening or results in a permanent injury that reduces quality of life. Deterministic effects are also called “tissue reactions." (Bold in the quotations above is the AIRP Working Group's)
The AIRP Working Group is well aware of the existence of differences in radiosensitivity among individuals; in this respect it must be pointed out that no radiation protection expert is supposedly so naïve as to think that thresholds for deterministic effects hold one and the same value for each individual exposed.
This said, the Working Group points out that the use of the adverb "generally" in paragraph (50) and in the definition in the Glossary when addressing the induction of tissue reactions does seem confusing; moreover, it is not in keeping with the rest of paragraph (50) and with paragraphs (52) and (53), where the existence of dose thresholds for tissue reactions is given as a fact.
Paragraphs 57, 310; Paragraphs 60, 77 from the ICRP document "Assessing Dose of the Representative Individual for the Purpose of Radiation Protection of the Public"
"(57) ... On this point, the Commission also emphasises that its estimates of nominal risk coefficients (Table 2 and Annex A) relate to contemporary human populations and depend upon current information on baseline disease rates, disease detriment and associated biological/clinical features. These factors are certain to change substantially over future generations and this adds to the implausibility of attempting to project the magnitude of radiation-associated disease far into the future."
"(310) ... In case of exposures taking place far in the future, additional uncertainties are involved. Thus dose estimates should not be regarded as measures of health detriment beyond times of around several hundreds of years into the future. Rather they represent indicators of the protection afforded by the disposal system."
Note: the paragraphs (60) and (77) below are quoted from the 27th December 2005 web version of the ICRP Document "Assessing Dose of the Representative Individual for the Purpose of Radiation Protection of the Public"
"(60) For a time period of about 50 years into the future, it is reasonable to assume that characteristics of individuals can be based on current habit data. The prospective assessment of annual individual dose can therefore be considered valid for a period of this order."
"(77) ... the dose constraint is set, at least in part, on the basis of exposures to individuals that are assumed to continue to occur for a number of years into the future. Most facilities are expected to operate for a period of at least 50 years. Therefore, it is the same individual being exposed for a number of years for whom compliance is being determined. ..." (Bold in the quotations above is the AIRP Working Group's)
The statements in paragraph 57 under comment are thought to be unquestionable; yet, on the basis of the ICRP considerations in paragraph (57) some might feel justified in arguing there is no point in making any estimate whatever of future detriment, e.g. for a waste repository. The Working Group feels that such a posture would mean driving to extremes the scientifically correct statement in paragraph (57), and accordingly would be unwarranted.
To avoid misunderstandings in a matter having obvious ethical implications, the Working Group suggests that ICRP should add to its statement in paragraph (57) and state, inter alia, what is the time span intended by "far into the future"; i.e. the time span where the Commission believes that projections of doses, i.e. doses to be received in the far future, can be thought of as being, broadly, a reliable measure of future detriment.
To this end, the AIRP Working Group points out that ICRP stated its position on this question of projections of doses into the future in paragraph (310) of the 2006 Draft Recommendations quoted above; guidance on the validity of projecting present data and estimates into the future is also given in paragraphs (60) and (77) of the above quoted ICRP Document on the representative individual where a 50-year-time span has been chosen.
Paragraph 71, Table 2, page 24
"(71) On the basis of these calculations the Commission proposes nominal risk coefficients for detriment adjusted cancer risk as 5.5 10-2 Sv-1 for the whole population and 4.1 10-2 Sv-1 for adult workers. For hereditary effects, the detriment-adjusted nominal risk in the whole population is estimated as 0.2 10-2 Sv-1 and in adult workers as 0.1 10-2 Sv-1. These estimates are shown in Table 2, where they are compared with the estimate of detriment used in the 1990 Recommendations in Publication 60 (ICRP, 1991b)."
"Table 2. Detriment adjusted nominal risk coefficients for cancer and hereditary effects (10-2 Sv-1)
Exposed population Cancer Heritable effects Total
Present1 Publ. 60 Present1 Publ. 60 Present1 Publ. 60
Whole 5.5 6.0 0.2 1.3 6 7.3
Adult 4.1 4.8 0.1 0.8 4 5.6
1Values from Annex A."
For a whole population and for a population of adults respectively, nominal probability coefficients are given by ICRP in paragraph (71) and in Table 2 as 5.5 10-2 Sv-1 and 4.1 10-2 Sv-1 for detriment adjusted cancer risk, and as 0.2 10-2 Sv-1 and 0.1 10-2 Sv-1 for hereditary effects.
With a view to making a comparison with the previous detriment estimates of Publication 60, in Table 2 ICRP reports the total measures of risk (cancer plus hereditary effects) for the two reference populations as 6 10-2 Sv-1 and 4 10-2 Sv-1 with no decimal digits. Reporting present total nominal risk estimates as rounded with no decimal digits is not felt to be entirely correct because Publication 60 estimates are given with one decimal digit in the same Table.
May it be pointed out in this respect that taking the sum of the detriment adjusted nominal risk coefficients for cancer and hereditary effects in single tissues or organs in the sixth column of Tables 4.1.a) and 4.1.b) of Annex A, the sum of such detriment adjusted nominal risk coefficients for cancer plus hereditary effects equates 5.74 10-2 Sv-1 for the whole population and 4.22 10-2 Sv-1 for a working age population, respectively. In this context, please also see Table 4.4 of Annex A where the sums of detriment adjusted nominal risk coefficients (cancer plus hereditary effects) for the whole population and adults are correctly reported as 5.7 10-2 Sv-1 and 4.2 10-2 Sv-1, respectively.
Other instances where some sort of rounding or perhaps of judgment was supposedly applied by ICRP are some of the values of nominal risk adjusted for lethality and life quality, which are reported in the fourth column of Tables 4.1.a) and 4.1.b) in Annex A, respectively for a whole population and an adult population.
If the rules of assessment laid down in Annex A are strictly applied, it follows that the nominal risk adjusted for lethality and quality of life in the fourth column of Table 4.1.a) of Annex A results, e.g., as 61.2 (not 61.9) for breast, 9.2 (not 8.8) for ovary, 10.2 (not 9.8) for thyroid in the case of a whole population. In addition to that, in the case of an adult population, there are even larger differences for some organs/tissues between the results of a strict application of the assessment rules for the nominal risk adjusted for lethality and quality of life laid down in Annex A and the values reported in the fourth column of Table 4.1.b) of the same Annex: e.g., 3.6 (not 3) for bone, 2.7 (not 3) for skin, 2.8 (not 3) for thyroid, 20.7 (not 20) for bone marrow, 11.6 (not 12) for gonads/hereditary. In this respect, it must be noted, though, that in both cases (whole population and adults) these operations of supposed 'rounding' do not result in any difference of note as regards detriment.
Owing to the well known uncertainties inherent in such a type of estimate, the differences between rounded and 'unrounded' values in Table 2 of the 2006 Draft and Tables 4.1.a) and 4.1.b) of Annex A can be thought of as lying within acceptable bounds. Nevertheless, it would be interesting to know whether we are dealing here with just an operation of 'rounding' by ICRP or whether some sort of sophisticated judgment is involved. The suggestion is that the Commission should clarify this point so as not to leave readers wondering.
Furthermore, with a view to avoiding the risk that the values in the Table might be quoted out of context, the Working Group suggests that footnotes to the values stating the differences in computation should be provided in the Table.
"(73) The present detriment-adjusted nominal risk coefficient for cancer shown in Table 2 has been computed in a different manner from that of Publication 60. The present estimate is based upon lethality/life impairment weighted data on cancer incidence," (Bold in the quotations above is the AIRP Working Group's)
ICRP points out in paragraph (73) that nominal risk coefficients for cancer were calculated in different ways in Publication 60, on the one hand, and in the 2006 Draft Recommendations and Annex A, on the other hand; the present estimate being given in the Draft as cancer incidence weighted by lethality and quality of life impairment versus cancer fatalities weighted by non fatal cancer, relative life lost for fatalities and life impairment in ICRP Publication 60.
In this connection, may it be pointed out that in the 2006 Draft Recommendations and Annex A the detriment adjusted nominal risk coefficients for cancer actually result from cancer incidence weighted for lethality, quality of life impairment and relative life lost as well, the latter factor having been left out in paragraph (73).
"(74) An additional point relating to the lethality-adjusted cancer risk of Table 2 is that during the period that these recommendations are likely to apply, the survival rates for many cancers are expected to rise. In this respect the nominal risk coefficient given will tend to be an over-estimate of risks in the future." (Bold in the quotation above is the AIRP Working Group's)
In connection with the term "lethality-adjusted cancer risk of Table 2" in paragraph (74) please see the comment under paragraph (73).
The AIRP Working Group feels that the statement in paragraph (73) (estimates of nominal risk coefficients being conservative because of expected improvements in survival rates in the future) might sound to some as having overtones of cynicism, although thought to be correct judging from present trends in the treatment of cancer. A further comments on the overestimate of nominal risk coefficients is that this amounts to taking account of survival only, while cancer, its treatment and the consequences involved are rather a complex and multifaceted phenomenon.
Page 49 Figure 2
"From a single source in normal, emergency, or existing controllable situations ... " (Bold in the quotation above is the AIRP Working Group's)
The AIRP Working Group is aware that Figure 2 is to be redrawn; anyhow the Working Group points out that the Commission now considers "planned" exposure situations in its three types of exposures, instead of "normal" situations.
"(152) The Commission is aware of the lack of certainty or precision in radiation dose models and efforts are undertaken to critically evaluate and to reduce them wherever possible. However, for prospective dose assessments and in particular for calculations of the effective dose in regulatory processes, the dosimetric models and parameter values that the Commission recommends for determining doses from quantitative information should be taken as reference models. These values have been fixed by convention and are therefore not subject to uncertainty. Equally the Commission considers that the dosimetric models and parameter values which are needed for the purpose of recommending dose limits or constraints are defined as reference data and, therefore, are not uncertain. ... " (Bold in the quotation above is the AIRP Working Group's)
The Working Group notes that ICRP has chosen not to address uncertainties in its dose models and parameter values, contending that such models and parameter values should be taken as reference values, and accordingly they should be considered as not being affected by uncertainty.
Yet, the fact remains that uncertainty, let alone variability, is obviously inherent in the choice of models and parameter values; moreover, other authoritative scientific institutions have chosen to address uncertainties affecting risk models. Thus, it would be extremely interesting, besides being correct from a scientific standpoint, if ICRP should make available to radiation protection experts an estimate of uncertainties across its models and parameters, perhaps in ad hoc publication.
Paragraphs 186, 214, 212, 289
"(186) Dose limits do not apply to medical exposures of patients, emergency situations, or to existing situations."
"(214) Protection of workers in existing exposure situations should follow the system for planned exposure situations."
"(212) The source-related dose constraint for occupational exposure in planned situations should be set for each source to ensure that the dose limit is not exceeded"
"(289) For historical reasons, however, such industries have not always operated completely within the Commission’s system of protection. Steps should be taken to bring these existing facilities within the Commission’s system. A decision should be made on whether it is justified to reduce exposures. This decision should also consider whether continued operation of the facility is also justified. When optimising protection, the constraint for occupational exposure should comply with the corresponding occupational dose limit, because occupational exposures are relatively straightforward to control. There may, however, be a number of issues surrounding public exposure, particularly to the accumulated waste residues from historical operations. Application of a constraint that complies with the Commission’s public dose limit, which is intended to be used in circumstances where radiological protection has been planned in advance, may lead to protective actions which are inappropriate for the health benefits obtained. The Commission considers that such public exposure situations may be considered as existing exposure situations with the value for the dose constraint being selected accordingly." (Bold in the quotations above is the AIRP Working Group's)
The Commission's guidance on dose limits in paragraph (186) seems to leave no doubt that dose limits are not supposed to apply, inter alia, to existing situations. Nevertheless, the 2006 Draft Recommendations state in paragraph (214) that protection of workers in an existing exposure situation should be considered as a planned exposure.
Furthermore, the guidance in paragraph (289) states that occupational exposure in existing facilities with naturally occurring radioactive materials (Section 7.2) should comply with the occupational dose limit, again considering such occupational exposures as subject for every purpose to requirements regarding dose limits for planned situations.
The Working Group shares the Commission's logic underlying the position in paragraphs (214) and (289); yet, since guidance cannot appear to be at variance, it is suggested that ICRP should express its intent in the very paragraph (186) as regards the application of dose limits to occupational exposures in existing situations, so that the guidance in paragraphs (186), (214) and (289) appears to be unswerving.
Paragraphs 184, 198, 200, 207, Glossary
"(184) The most fundamental level of protection, therefore, is the source-related restriction to the dose that individuals may incur, namely the dose constraint. ... The dose constraint is used to provide a level of protection for the most highly exposed individuals from a single source within a class of exposure and within an exposure situation. The Commission recommends the use of quantitative dose constraints to protect the most highly exposed individuals from the relevant sources. ... ."
"(198) The most fundamental level of protection is the source-related restriction called a dose constraint, or risk constraint for potential exposures (see Chapter 8). ... They are used to provide a level of protection for the most highly exposed individuals from a single source within a type of exposure. ... The Commission recommends the use of quantitative dose constraints to protect the most highly exposed individuals from all identified controllable sources."
"(200) The dose constraint is related to one source under each particular circumstance, which can be either a planned situation, or an emergency situation, or a situation of existing exposure."
"(207) In all cases the bands for dose constraints are specified in terms of projected incremental individual doses. The Commission’s upper value for a constraint of 100 mSv is set so as to restrict or avoid the probability of significant health effects and, as such, should be considered to apply to the total dose to an individual from all sources. In most such instances, however, one source will be dominant and the upper value could be applied to that source."
"(Glossary) Dose constraint: A prospective and source related restriction on the individual dose from a source, which serves as an upper bound on the dose in optimization of protection for that source. ... For public exposure, the dose constraint is an upper bound on the annual doses that members of the public should receive from the planned operation of any controlled source." (Bold in the quotations above is the AIRP Working Group's)
The Working Group notes that the dose constraint is repeatedly defined with reference to a single source in paragraphs (184), (198) and (200). Yet the Commission states in paragraph (207) as well as in the Glossary, though to a less clear extent, that the 100 mSv constraint for public exposure is an upper bound to be applied to the total dose from all sources, owing to the obvious need to protect individuals from the occurrence of deterministic effects and from enhanced risks of stochastic effects in emergency and existing exposure situations.
The Working Group is in no doubt on the soundness of the Commission's guidance that the 100 mSv dose constraint should relate to exposures from all sources. Yet, since the nature of this dose constraint in respect of all other constraints is very specific, it being an upper bound applying to exposures from all sources, the suggestion is that the Commission's reasons for the choice on the particular nature of the 100 mSv upper bound should be set out in the very paragraph (184), where the dose constraint is first discussed.
An additional suggestion is to weigh whether the 100 mSv "dose constraint" could perhaps be straightforwardly referred to in a specific way, e.g. "maximum dose constraint for exposures from all sources". This would have the effect of emphasising right away that the 100 mSv constraint value is related to exposure from all sources, without paying the price of introducing yet another name for a new, albeit slightly different, type of dose constraint.
"(205) The second band, from 1 mSv to 20 mSv, applies in circumstances where individuals receive direct benefits from an exposure situation but not necessarily from the exposure or the source of the exposure, itself. Constraints in this band will often be set in circumstances where there is individual surveillance or dose monitoring or assessment, and where individuals benefit from training or information. Examples are the constraints set for occupational exposure in planned situations. In the event of an accident, countermeasures such as sheltering and iodine prophylaxis would fall within this band." (Bold in the quotation above is the AIRP Working Group's)
As regards paragraph (205) on the second band of constraints (1 to 20 mSv per year), the Working Group feels that it is somewhat difficult to identify categories of individuals receiving direct benefit from an exposure situation, and to whom the second band of constraint values can apply.
While radiation workers and radon home dwellers fall in this second band in that they can be thought to receive direct benefit by the exposure situation, though not by the exposure itself, there are doubts on the example regarding countermeasures in an accident at the bottom of paragraph (205). As a matter of fact, it is by no means easy to make out how individuals can possibly be thought of receiving direct benefits from a situation if these individuals are affected by an emergency situation needing countermeasures like sheltering or iodine prophylaxis.
It certainly is both sound and expedient advice that those individuals involved in such an emergency situation should be included in this second constraint band. Still, if the criterion for inclusion in the 1 to 20 mSv band is that of receiving a direct benefit from the exposure situation, it is suggested that the Commission should expand on the rationale for including in this band individuals who are involved in an emergency situation needing the above mentioned countermeasures.
Paragraphs 213, first dash, 86, 112, 144
"(213)... - Otherwise, for rescue operations involving the prevention of serious injury or the development of catastrophic conditions, every effort should be made to avoid serious tissue injuries by keeping doses below about 1000 mSv and, ideally, to avoid other tissue injuries by keeping doses below 100 mSv, the Commission's maximum value for a constraint."
"(86) ... However, the Commission notes ... that the LSS data are consistent both with there being no dose threshold for risks of disease mortality and with there being a dose threshold of around 0.5 Sv."
"(112) ...The unit of effective dose is J kg-1 with the special name sievert (Sv). The unit is the same for equivalent dose and effective dose as well as for some operational dose quantities ... . Care must be taken in ensuring that the quantity being used is clearly stated"
"(144) In cases of high doses that could give rise to tissue reactions the use of effective dose is completely inappropriate." (Bold in the quotations above is the AIRP Working Group's)
It is pointed out that the use of the sievert unit ought to be avoided altogether in connection with such exposure values as 0.5 Sv in paragraph (86) and 1,000 mSv in paragraph (213), as per the guidance in paragraph (144). It is thought that the gray unit ought to be used in its place in both statements, because equivalent and effective doses should only be employed in the low dose range, i.e. it is felt that the Sv unit should not be used above 100 mGy.
In addition, since the guidance in paragraph (213) to keep exposures for rescue operations uses values expressed in mSv ("below about 1000 mSv"), the Working Group feels that the mSv unit is ambiguous in this context given that radiation protection as well as operational quantities are expressed in sieverts, and it is not entirely clear from the context which quantity is addressed in the statement in paragraph (213).
The Working Group realises the manifold implications, metrological and other, related to changing the names of radiation protection units; nonetheless, it suggests that the Commission should consider whether, all in all, it would be possible to give a special name to the unit of effective dose, with a view to distinguishing values expressed in effective dose from the start.
Paragraphs 226, 45, 148; Section 5.9 of Annex B
"(226) The best option is always specific to the exposure situation and represents the best level of protection that can be achieved under the circumstances. Therefore it is not relevant to determine, a priori, a dose level below which the optimisation process should stop. Depending on the exposure situation, the best option could be close to or well below the appropriate source-related constraint. This means that the optimisation process may result in doses lower than any level that could be proposed as an “entry level” into the system of radiological protection."
"(45) Certain practices and sources (that in principle are subject to radiological protection regulations) may be exempted from some requirements because their control is not warranted. The principles that should govern the process of exemption are the following:
• the individual risk attributable to the radiation exposure caused by an exempted practice or source must be insignificant (for man-made sources, this is judged to correspond to an annual dose of around 10 mSv);
• radiological protection, including the efforts for the regulatory control, must be optimised; and,
• the practice must be justified and its sources should be inherently safe."
"(148) To avoid aggregation of, e.g., very low individual doses over extended time periods and wide geographical regions, limiting conditions need to be set. The dose range and the time period should be stated."
Note: the following paragraph is quoted from Section 5.9 of the 12th February 2006 web version of Annex B.
"5.9 ... The Commission considers that in the low dose range the risk factors have a high degree of uncertainty. This is particularly the case for very low individual doses which are small fractions of the radiation dose received from natural sources. The use of collective dose under such conditions for detailed risk estimates is not a valid and reasonable procedure. In this sense it might be considered that individual doses of less than 10 μSv per year (see MC document) are negligible and should not be included into the assessment of collective dose." (Bold in the quotations above is the AIRP Working Group's)
The Commission's rationale on optimisation, stated in paragraph (226), seems clear, i.e. there is no de minimis or entry level of dose, determined a priori, below which optimisation should stop.
The Working Group points out, however, that there seems to be conflicting ICRP guidance on this subject. In fact, the Commission has also taken quite a different, and persuasive, view in paragraph (45) of the 2006 Draft Recommendations, i.e. that a low level of individual dose, e.g. 10 µSv per year, could be considered as insignificant for exemption purposes. ICRP guidance for exemption of small sealed sources in paragraph (295) is in the same vein.
In respect of collective dose, which is thought in paragraph (147) to be "mainly an instrument for optimisation", ICRP thinking follows a similar pattern, since in paragraph (148) the Commission recommends that limiting conditions need to be set for the dose range over which collective dose should be integrated.
Also, in Section 5.9 of Annex B the Commission has taken the view that a low level of individual dose, of less than 10 µSv per year, is negligible and should not be included in the computation of collective dose, owing to the reasons stated in the Annex about uncertainties in the risk factors, and, it may be added, to uncertainties in the very estimates of doses.
It is felt that the Commission's position on a de minimis level of dose for optimisation and exemption should be harmonised.
Paragraphs 232, 233
"(232) ... The implementation of the process of optimisation of protection is the responsibility of the operating management, subject to the requirements of the authority. An active safety culture supports the successful application of optimisation by both the operational management and by the authority."
"(233) ... An open dialogue must be established between the authority and the operating management, and the success of the optimisation process will depend strongly on the quality of this dialogue." (Bold in the quotation above is the AIRP Working Group's)
With a view to achieving a successful application of optimisation the Working Group feels that in the contest of safety culture in paragraph (232) the need should be emphasised that all subjects with operational roles in radiation protection, like e.g. radiation protection officers and physicians, should have educational curricula and training adequate to their functions. The need for education and, broadly, for information is felt to be of the essence, as is pointed out in the comment on paragraph (327).
Besides, the Working Group suggests that in paragraph (233), besides the dialogue between the authority and management, the involvement of stakeholders should be mentioned, in that dialogue between all concerned parties is one of the keys to success as regards optimisation.
Table 4 "Framework for source-related dose constraints with examples of constraints for workers and the public from single dominant sources for all situations that can be controlled (effective dose in a year). "(Bold in the quotation above is the AIRP Working Group's)
The Working Group feels that two comments should be made as regards the caption of Table 4. Firstly, the 100 mSv constraint is applicable not only to exposures from single dominant sources, as shown in the caption, but to exposures from all sources as well, as per the guidance in paragraph (206); accordingly, the latter feature should be specified. In this respect please see the comment on paragraph (207).
Secondly, the caption specifies that values in the Table refer to effective dose in a year; this does not appear correct because in two cases the recommended maximum values of constraints (1 to 20 and 20 to 100 mSv) in the first column of the Table may well relate to acute exposures as well.
"(242) The Commission’s multi-attribute approach to the selection of dose limits necessarily includes societal judgements applied to the many attributes of risk. These judgements would not necessarily be the same in all contexts and, in particular, might be different in different societies. It is for this reason that the Commission intends its guidance to be sufficiently flexible to allow for national or regional variations. ... " (Bold in the quotation above is the AIRP Working Group's)
The statement in paragraph (242) is thought to be very wise and it actually has general implications above and beyond the specific aspect of dose limits. Nonetheless, the Working Group wonders whether in this context the Commission might consider recalling the opportunity for harmonisation among the various States as it would be of great help for the credibility and acceptance of the radiation protection system.
Table 5 Recommended dose limits
The Working Group welcomes the Commission's decision to recommend dose limits unreservedly in that it greatly contributes to the stability of the protection system.
Like in Publication 60 the Commission continues to recommend two types of dose limits for the public, i.e. a limit on effective dose and two limits on annual equivalent dose to the lens of the eye and to the skin. In this context, the Working Group is aware of the inherent variability in individual sensitivity to radiation; still, it wonders whether the Commission might care to address a question that has often been asked, i.e. the rationale underlying the choice of reducing the equivalent dose limits to the lens and the skin of workers by a ten fold factor when recommending equivalent dose limits to the same tissues/organs for the public.
"(258) In radiotherapy, optimisation involves not only delivering the prescribed dose to the tumour, but also planning the protection of tissues outside the target volume (Publication 44, ICRP; 1985)."(Bold in the quotation above is the AIRP Working Group's)
The Working Group submits two comments. Firstly, paragraph (258) addresses therapy and appears to be quite out of place in Section 6.2.1 addressing diagnostic reference levels and should be moved e.g. to Section 6.2 above. Secondly, "radiotherapy" or "radiation therapy" has become a synonym of radiation treatment by means of external irradiation, see in this respect ICRP Publication 86.
Since the same concept stated in paragraph (258) applies equally well to other types of therapy, i.e. therapy by means of unsealed radioisotopes in nuclear medicine, it is suggested that a different term should be used in its place, e.g. an ad hoc definition should be included in the Glossary.
"(259) In principle, it might be possible to choose a lower reference level below which the doses would be too low to provide a sufficiently good image quality. However, such reference levels are very difficult to set, because factors other than dose also influence image quality. Nevertheless, if the observed doses or administered activities are consistently well below the diagnostic reference level, there should be a local review of the quality of the images obtained." (Bold in the quotation above is the AIRP Working Group's)
Even though an ad hoc ICRP publication on medical radiation is forthcoming, it is felt that in 2006 Draft Recommendations emphasis should be given to the importance of adopting and consistently enacting appropriate quality assurance policy and procedures, since quality assurance is of paramount importance for a correct application of radiation for medical purposes.
"(279) In cases where action to reduce doses is recommended, the process of optimisation below a constraint should be followed. The Commission has previously provided guidance on selecting an action level for protection against radon (see section 8.4), as well as for protection against other natural sources (ICRP 65, ICRP 82). These action levels are effectively constraints i.e., levels of aspiration often set by national authorities and not a mandatory level which must be achieved. In circumstances where doses exceed the value of constraints, optimised protective actions should be taken to reduce doses. Below the relevant constraint, action may be undertaken if technically easy and not entailing excessive cost, to reach an optimised level of exposure. In contrast to action levels below which no action is required, the process of optimisation and constraints do not use any predetermined end point below which no action is warranted to reduce the dose further." (Bold in the quotation above is the AIRP Working Group's)
The Working Group believes that some aspects in paragraph (279) regarding the optimisation principle and the application of constraints to exposures to sources of natural origin should be clarified by the Commission.
Firstly, the Commission states in the guidance given in paragraph (279) of the 2006 Draft Recommendations that if the situation justifies taking action with a view to reducing doses, then the process of optimisation below constraints should be followed. And yet, a few lines below it appears that the way the process of optimisation should be applied for existing exposures from natural sources takes on some specific features rather different from what it would be expected.
In fact, the guidance in paragraph (279) states that where doses are above the relevant constraint then "optimised protective actions should be taken to reduce doses"; however, if doses are below the relevant constraint then the guidance states that "action may be undertaken if technically easy and not entailing excessive cost, to reach an optimised level of exposure".
Assuming that "optimised protective actions" stand for the application of the optimisation principle as stated at the start of paragraph (279), the Working Group notes that in the second instance where action might be taken (doses below constraints) the optimisation principle takes on rather an atypical look, which closely reminds the principle of keeping doses "as low as readily achievable" of ICRP Publication 9, and which is different from the way the optimisation principle is now stated.
Secondly, in paragraph (279) the Commission reminds that action levels had previously been recommended, e.g. for protection against radon, and states that "These action levels are effectively constraints". The Working Group is not clear as to what is meant by the Commission in that the meaning of action levels is markedly different from present constraints: below an action level no action is required while being below a constraint does not imply per se that no action may be warranted, as the Commission itself efficaciously reminds in the last sentence of the paragraph.
Paragraphs 280, 44
"(280) In many cases it will be obvious that action to reduce exposures is not warranted. This conclusion will often be intuitive. Principles for exclusion and exemption of natural sources are that the individual risk from the source or practice is insignificant, radiological protection is optimised, or the sources are inherently safe and the practice is justifiable. ... "
"(44) Exposures that may be excluded from radiological protection legislation include uncontrollable exposures and exposures that are essentially not amenable to control regardless of their magnitude. ... "
"(294) Many natural radiation sources are not amenable to control in that they are unavoidable or uncontrollable, at least without inordinate effort, or while theoretically controllable are not feasible to control. ... " (Bold in the quotations above is the AIRP Working Group's)
The Working Group suggests that the Commission should review the guidance given in paragraph (280) on the criteria governing exclusion of natural sources from the protection system: i.e., individual risk from the source or practice is insignificant, radiological protection is optimised, or the sources are inherently safe and the practice is justifiable. In point of fact, the statement in paragraph (280) raises doubts in the light of the guidance in paragraph (44) of Section 2.4 on Exclusion and Exemption and in paragraph (294) of Section 7.3 on the Controllability itself of natural sources.
As a matter of fact, as paragraph (280) now stands, the criteria for exclusion of natural sources from the protection system are unquestionably at variance with the guidance given on exclusion in paragraph (44), which appears to be of an entirely general nature; as a result, the criteria for exclusion of natural sources are mistaken for the exemption criteria.
"(292) ... members of the public make a distinction between natural and man-made exposure and weigh highly those radiation risks attributable to technological sources, claiming stronger protection for those sources. This has resulted in a dichotomous scale of protection depending on the origin of exposure. ... " (Bold in the quotation above is the AIRP Working Group's)
The statement in paragraph (292) that the public takes a dichotomous view as regards exposures to, and protection from, natural and man made sources is felt to be true, at least to a rather large extent. However, the Working Group is unclear about the implications of this statement on how exposure to natural sources is addressed by the Commission in the subsequent paragraphs.
In addition, it is felt that risk perception by members of the public has a far broader impact than the dichotomy of public reaction to exposures from man made versus natural sources; in actual fact, the impact of risk perception is of a general nature so as to become a significant factor, of which decision makers have to take account, resulting in economic and social implications of great consequence.
It is suggested that the Commission should weigh the inclusion of risk perception at the start of the Recommendations, perhaps when addressing Exclusion and Exemption in Section 2.4 of the 2006 Draft Recommendations.
"(294) ... Examples of sources which should be excluded are cosmic rays at ground level, 40K in the human body and unmodified concentrations of naturally occurring radionuclides in most materials, except food stuffs, drinking water and animal feed, below 1000 Bq/kg for the heads of uranium and thorium series and 10,000 Bq/kg for 40K. Due to the wide variations in residential radon concentrations between regions, exclusion levels should be set 40 Bqm-3, i.e. the global mean indoor radon concentration The Commission recommends that such sources are excluded from the radiation protection system. ... " (Bold in the quotation above is the AIRP Working Group's)
ICRP recommends in paragraph (294) that naturally occurring radionuclides in most materials, aside from food stuffs, drinking water and animal feed, should be excluded when their concentrations lie below 1,000 Bq/kg for the heads of the uranium and thorium decay series and 10,000 Bq/kg for 40K.
The Working Group notes in this respect that the European Union issued guidance (European Commission, Radiation Protection 112, Radiological Protection Principles concerning the Natural Radioactivity of Building Materials, 1999) on the use of building materials containing natural radionuclides.
Using the model and the parameter values set forth in the European Union RP112 publication cited above and assuming a room made of concrete having the above reported concentrations in 238U, 232Th and 40K, the Working Group points out that an individual would be likely to incur an annual effective dose of about 13.6 mSv in excess of background.
Besides, the Working Group points out that paragraph 5.1 of the relevant IAEA guidance (IAEA Safety Guide no. RS-G-1.7) sounds a note of warning in respect of an indiscriminate use of the exclusion concentration values of natural radionuclides, notably as regards building materials.
The Working Group suggests that the Commission should weigh whether concentration levels for exclusion of naturally occurring radionuclides in building materials should be specifically addressed in the new Recommendations.
"(295) National authorities should determine activity concentration or activity levels for exemption for any amount of non-edible material and for moderate amounts of non-edible material, for food and drinking water, and for material in the form of a sealed source with a dose rate less than 1 µSv/h at a distance of 0.1m (see Section 2.2.)." (Bold in the quotation above is the AIRP Working Group's)
The Working Group has doubts whether the mention of sealed sources (with a dose rate less than 1 µSv/h at a distance of 0.1 m) as candidates for exemption is proper in paragraph (295) since Section 7.3 addresses in essence controllability of existing exposures to natural sources. While there certainly exist manufactured sources, e.g. for calibration purposes, containing radioisotopes of natural origin which are still used as a matter of routine in laboratories etc, it is doubtful that such sources should be classified as a case of existing exposure. Accordingly, it is felt that their possible exemption should be addressed under the heading of planned exposure situations.
A further related question is why the general criteria for exemption stated in paragraph (45) are not thought to be adequate by the Commission and a specific mention of sealed sources with natural radionuclides is felt as necessary in paragraph (295).
Paragraphs 297, 298, 301
"(297) The Commission’s view on radon risk assessment has, up till now, been that it should be based on epidemiological studies of miners. Given the wealth of data on domestic exposure to radon, the Commission now recommends that the estimation of risk from domestic radon exposure be based on the results of pooled residential case control radon studies. ... "
"(298) ... The Commission issued the current recommendations for protection against radon-222 at home and at work in Publication 65 (ICRP, 1994a). The policy has found wide acceptance and the present recommendations broadly continue the same policy."
"(301) The Commission reaffirms the basic principles for controlling radon exposure as set out in Publication 65 (ICRP, 1994a). Even though the nominal risk per Sv has changed slightly, the Commission, for the sake of continuity and practicality, retains the relationship between the constraint of 10 mSv given in Publication 65 and the recommended corresponding activity concentration. ... " (Bold in the quotations above is the AIRP Working Group's)
The Working Group appreciates the philosophy of continuity and practicality in the Commission's guidance on the control of radon exposures recommended in paragraphs (298) and (301).
The Working Group points out that the guidance in paragraph (297), on the one hand, and in paragraph (301), on the other hand, appear to be somewhat at variance. The Commission states in paragraph (297) that pooled residential case control studies on radon exposures will make up from now on the basis for radon risk estimates, although this downright assertion seems to be questioned to some extent by the statement in paragraph (298).
Then, in paragraph (301) the Commission goes on to outright confirm the numerical guidance given in Publication 65, thus setting forth the same Publication 65 radon exposure action levels that were based on results from cohorts of miners. In this context, it would appear from paragraph (301) that radon constraints were recommended in Publication 65 while, if truth be told, radon action levels were recommended in the Publication. In this respect, please also see the comment on paragraph (279).
Another aspect that is believed to be worth mentioning is that an in depth discussion of available results from scientific literature on radon exposure is missing in the Draft Recommendations, and in this respect Annex A does not shed much light either; for instance, no mention is made of radon risk estimates from BEIR reports.
The Working Group feels that the guidance on radon exposures should be expanded upon with a thorough critical assessment of available scientific results.
Paragraphs 318, 319, 317
"(318) Risk constraints, like dose constraints, are source-related and in principle should equate to a similar health risk to that implied by the corresponding dose constraints for the same source. However, considering the uncertainties in estimations of the probability of an unsafe situation and the resulting dose, it will often be sufficient, at least for regulatory purposes, to use a generic risk constraint value based on generalisations about normal occupational exposures, rather than a more specific study of the particular operation. For occupational exposures, the Commission continues to recommend a generic risk constraint of 2 10-4. For potential exposures of the public, the Commission retains a risk constraint of 10-5, as in the case of disposal of long-lived radioactive waste (ICRP 1998)."
"(319) The use of probability assessment is limited by the extent that unlikely events can be forecast. The estimates of annual probabilities of initiating events much less than 10-6 must be treated with doubt because of the serious uncertainty of predicting the existence of all the unlikely initiating events. In many circumstances, more information can be obtained for decision making purposes by considering the probability of occurrence and the resultant doses, separately."
"(317) Conceptually, the simplest way of dealing with the potential exposure of individuals is to consider the individual probability of radiation-related death, rather than the effective dose (ICRP, 1997). For this purpose, the probability is defined as the product of the probability of incurring the dose and the lifetime conditional probability of radiation-related death from the dose if it were to have been incurred. The resulting probability can then be compared to a risk constraint." (Bold in the quotations above is the AIRP Working Group's)
The Working Group welcomes the Commission's recommending values for generic risk constraints since they can be of help for practical radiation protection, particularly in not overly complex installations. Also, the Working Group is in agreement with the Commission's pointing out in paragraph (319) that a separate consideration of the probability of occurrence of a potential exposure and of its consequences in terms of doses to be incurred is likely to be more helpful in many situations; in this case, more attributes of an accident can be weighed, like the number of individuals affected should the accident happen.
Furthermore, the Working Group suggests that the Commission should at least include a specific Glossary entry with a view to defining the quantity "lifetime conditional probability of radiation-related death" employed in paragraph (317), as well as the quantity "lifetime unconditional probability of radiation-related death". It is pointed out in this connection that a specific Annex (Annex C) addressed these measures of radiation risk in Publication 60.
"(327) The response must essentially be to identify and characterise the emergency situation, to provide medical care for injured persons, to attempt to avoid further exposures, to gain control of the situation, to prevent the spread of radioactive materials, to provide accurate and timely information to the public, ... , while dealing with psychological issues ... " (Bold in the quotations above is the AIRP Working Group's)
In paragraph (327) of Section 8.5, where the Commission gives guidance on exposures with malicious intent, the AIRP Working Group feels that some further aspects should be mentioned with a view to increasing the effectiveness of response. For instance, threats should be screened by skilled personnel in order to evaluate their seriousness, and ad hoc medical teams should be set up and made available out of hospitals for a prior screening of supposedly injured persons so as to avoid hospital facilities being overcrowded.
"(350) It is important that decision makers inform the public of all aspects of their decisions, otherwise the public may be misled and the radiological protection efforts may be mistrusted." (Bold in the quotation above is the AIRP Working Group's)
The Working Group believes it to be important that both the public and all of those playing a role in emergency and existing exposure situations should also receive prior information on radiation, its effects, protection principles, and criteria for intervention and mitigation adequate to their role.